1987 Fiscal Year Final Research Report Summary
Adaptive strategy of the Late Cretaceous ammonites inhabited offshite waters.
| Project/Area Number |
61540577
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Stratigraphy/Paleontology
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| Research Institution | Waseda University |
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Principal Investigator |
HIRANO Hiromichi Institute of Earth Science, School of Education; Progessor, 教育学部, 教授 (00037293)
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| Project Period (FY) |
1986 – 1987
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| Keywords | Cretaceous / Ammonites / Offsdhore fauna / Desmoceras / Tagodesmocetoides / Homeostasis / ホメオスタシス |
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| Research Abstract |
Many specimens of Genus Desmocerar and Tragodesmoceroides(Mollusca,Ammonoidea) which range the Cenemanian and the Turonian(Cretaceous) respectively were obtained from the Obira, The Oyubari and some other additional aread with detailed stratigraphic records.
The cross and the tangential sections were at first made, and relative growth analyses were carried out for all population samples on some main characters which controll the morphology. The chronocline of each characters-set is mode clear for each species in each area through the biostatistical traatment on the basis of popuation concept. These chronoclines are regarded to be the essential pattern of the morphological evolution because the geographic variation of each character is not large and these data are obtained from the main area of the geographical distribution.
These analytical results leas me to the conclustion that the Turonian Tragodesmoceroides subcostatus evolve from the Cenomanian Desmovers japonicum only with ther change of the surface ornamentation. This phyletic speciation proceeded in a geologically instantaneous time at the boundary between the cemomanian and the Turoniam. The morphology of D. japonicum is homeostatic through the duration of the species.
The tTuronian tragodesmoceroides subcostatus is believes to be ont species in the age. I. clatified that is speciatrd by the end oft the middle Turonian in terms of the habitat segregation. The newly speciated speceis exclusibely occurs in somewhat shallower facies. Again these two speicies of Tragodesmocetoides show motphological homeostasis throught the duration, and the geographic speciation took place instantaneously.
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